Landfill sites are utilized for the disposal of waste. In the usual case, the landfill site is required to have a water-impermeable bottom. Oxygenated groundwater or leachate is circulated through the landfill. Sometimes the leachate is sprayed onto the top of the landfill site and is oxygenated during the spraying process. This oxygenated water or leachate then passes through the material of the landfill and causes desired oxidation with accompanying desired decomposition of materials within the landfill. Typically, the decomposition produces methane gas, which can be a useful by-product of the landfill site.
There is a requirement that the leachate within the landfill site be pumped. Otherwise, the leachate will fill the site, lose its oxygen content to the oxygen demanding environment of decomposing material of the landfill, and thereafter prevent the desired circulation of oxygenated water through the landfill. By the expedient of pumping the leachate from the water-impermeable bottom of the landfill, aerating the leachate by passing the leachate through conventional sprinklers, and allowing the leachate to recirculate through the landfill, systematic and desired decomposition of the materials within the landfill occurs.
Pneumatic pumps are often preferred relative to electric pumps in such landfill applications for several reasons. First, in landfill applications, it is not possible to predict the flow rate at any individual pump. Pneumatic pumps can accommodate a wide range of flow rates; electric pumps are more restricted due to the fact that their driving motors are usually run at a constant speed.
Secondly, the leachate contains particulate matter. Pneumatic pumps are much more tolerant of particulate matter than electric pumps. Electric pumps can jam or wear excessively when encountering particulate matter; pneumatic pumps can undergo one or more imperfect cycles and then pass the particulate matter through the pump.
Third, the flow of the leachate is not always constant. The flow can either be extremely low or erratic. Electric pumps in accommodating periods of low flow often start and stop frequently. This can and does cause such pumps to become overheated and burn out.
Fourth, leachate can be extremely corrosive. Electric pumps with their required electrical connections accommodate the corrosive leachate with difficulty; pneumatic pumps because of their simplicity can be given a higher tolerance to the corrosive leachate.
Fifth, electrical connections are difficult to install in landfill sites. Specifically, the electrical connections must pass across landfill sites to each well site. Because of the dynamic decomposition occurring, levels of the landfill constantly change requiring constant attention to rerouting of the electrical connections. Further, and because of the content of the landfill, the leachate is frequently conductive. As a consequence, down-hole electrical connections in the individual wells to power such pumps are much more difficult to maintain than pneumatic connections.
As applied to landfill leachate recirculation, pneumatic pumps have a serious drawback. Typically, it is desired to have the input to such pneumatic pumps as close to the bottom of the landfill leachate groundwater table as possible. The pneumatic pumps of choice operate on a "float-triggering" principle in connection with a lever and stainless steel poppet air valve (see U.S. Pat. Nos. 5,487,647 (Breslin); 5,358,038 (Edwards, et al.); and 5,358,037 (Edwards, et al.)). The float vertically reciprocates from a lower, intake position to an upper, pump actuation position in response to the level of leachate which enters the pump from the soil immediately surrounding the pumps. While an electric pump can have an inlet immediate to the bottom of the groundwater table, pneumatic pumps because of the requirement of float actuation must have a so-called "trigger depth." This trigger depth is the required submergence of the pump necessary to actuate a pump cycle.
The necessity of this trigger depth requires a static head of leachate of a minimum depth before a pumping cycle can be initiated. Unfortunately, the greater the trigger depth, the larger the volume of leachate which is maintained at the bottom of the landfill. It is desired to keep the volume of leachate at the bottom of the landfill site to a minimum. With current intake check valve designs on such pumps, trigger depths are over 12 inches. Certain laws now require such trigger depths to be 12 inches or less.
In the disclosure that follows, I utilize a radial check valve array to lower the trigger depth of a pneumatic pump. The reader will understand that although such radial check valve arrays are known, they have not been utilized or suggested to be utilized for lowering the trigger depth of pneumatic pumps. This is especially true as these pneumatic pumps are applied to the problem of leachate in landfill sites. Accordingly, I claim invention in this combination.